The current process is rather tedious but it is possible. There are two main stages.
Stage One: Old Quiz to New Quizzes (careful on images)
If the old quiz uses random pull from a question bank then build a version in classic quizzes which pulls all of the questions from the question bank. Next, go to settings and export the quiz. This will create a QTI. Save this export to your local drive.
Go to New Quizzes Item Banks. Create a new item bank. You can name it anything. Enter the item bank. Click on the 3 vertical dots (the kabob). You'll see import content. Import in the QTI that you exported. The new item bank will be renamed the name of that QTI export.
Stage Two: Copy Questions from Item Bank to Item Bank
Now you have TWO item banks in New Quizzes. Choose which will hold all of the questions. I'll assume the first item bank, therefore, open the new item bank. Click on the Copy Icon (not the pencil or trash can). Search for the first item bank name. Keep the content in case there is a mistake. Repeat through each of the questions. When you are done then you should have one item bank with all the questions from the classic and the new quizzes.
